Mika McKinnon

The SpaceX Dragon capsule splashed down this afternoon, returning over 3,500 pounds of cargo back to Earth from the International Space Station. By completing its 3rd freighter mission, the Dragon brings the gift of over 1,600 pounds of scientific samples and hardware awaiting detailed analysis.

Splashdown in the Pacific Ocean. Image credit: SpaceX

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Launched on April 18th with the Falcon 9 rocket, the Dragon capsule brought 4,969 pounds of cargo up to the International Space Station. Between launch and splashdown, the capsule has been away for 29 days, 23 hours and 40 minutes, the longest Dragon mission yet.

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Along with the usual load of fresh supplies and new hardware, two pieces of cargo from the resupply mission needed to be plucked from the Dragon using the space station's robotic assistant, Dextre. Dextre unloaded a high-definition camera suite and an optical laster communications terminal. The equipment pair is being used to capture a high-definition footage from the space station, then stream it back to ground antenna on Earth to give all of us trapped planet-side a glimpse of the stunning view.

The Dragon was unbolted and hauled away from the space station by the gigantic robotic arm before being released and sent home this morning. Everything went exactly as planned, splashing down off the coast of Baja this afternoon to complete the third of 12 resupply missions SpaceX has contracted to perform for NASA.

The Dragon and its cargo, safely retrieved from the Pacific and aboard a ship to head home. Image credit: NASA

The Dragon carries a heavy load of planned scientific samples awaiting full analysis, but also some detritus from the consequences of having people living in space: a spacesuit needing repairs, and water from the malfunction that tried to drown an astronaut last summer. In total, the robotic cargo freighter is returning 3,563 pounds of material to Earth in its pressurized hold. Broken down by category, that's just over 1,600 pounds of scientific hopes and dreams in the form of samples and research hardware, just under 1,200 pounds of crew and vehicle supplies, and 627 pounds of spacewalk tools.

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While a lot of science can be conducted aboard the space station, some of the samples need to return to Earth for full analysis. This shipment includes drug-resistant bacteria that will be compared to its terrestrial cousins, plants stressed out by growing in microgravity,

The MicroRNA Expression Profiles in Cultured Human Fibroblasts in Space (Micro-7) study is looking at human fibroblasts. Considering that these cells make up most of the human body, understanding how microgravity impacts DNA damage and repair in fibroblasts will help in predicting the impact of spaceflight on organs, tissues, and the rest of the human body.

The Antibiotic Effectiveness in Space (AES-1) investigation compares E. coli here at home and in orbit after a previous experiment discovered that bacteria can grown in space even when doused in antibiotic concentrations that would usually smother them. With a bit of luck, this experiment will shed some light on why antibiotics have decreased effectiveness in spaceflight, and maybe even help understand how to combat antibiotic resistance here on Earth.

Sticking to the bacterial theme, on the outgoing trip Dragon had delivered hardware for the Biological Research in Canisters (BRIC) space station facility: BRIC-18-1 and BRIC-18-2. BRIC-18-1 is growing antibiotic-resistant strains of Bacillus subtilis, found in soil, and Staphylococcus epidermidis, found on the skin, on the station. They'll be compared to terrestrial control samples to see if spaceflight triggered any mutations.

BRIC-18-2 leaves the bacterial theme, growing seedlings in space to see how space messes with them. Preserved seedlings made the return journey so researchers can poke at them to determine the impact of gravity, radiation, vibration and limited exchange of gases on their growth.

While it's named the Advanced Plant Experiments-02-2 (APEX-02-2), the next study on the list does not mean Dragon was carrying two batches of seedlings. APEX-02-2 used brewer's yeast, Saccharomyces cerevisiae, to check out how the cells adapted to the space environment during their time in microgravity. If researchers can tease out exactly which mechanisms are regulated by the genes that are impacted by growth in microgravity for this simple organism, those ideas might help understand the molecular responses of more complicated cells in the same environment.

The next set of samples continue to look at changes in gene analysis, but get more directly to the impact of spaceflight on humans. The T-Cell Activation in Aging investigation (which lacks a not-so-catchy acronym) is trying to identify the defect in T-cell activation in microgravity, which may have implications for combatting the decline of T-cells and the immune system during the aging process.

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A boat will carry the Dragon and its cargo to a port near Los Angeles. Some of the cargo, particularly the freezer of research samples, will be peeled out and delivered to NASA within 48 hours. The rest of the craft will be returned to SpaceX's test facility in McGregor, Texas.